@mixin abs-pos($top: auto, $right: auto, $bottom: auto, $left: auto) {
    top: $top;
    right: $right;
    bottom: $bottom;
    left: $left;
    position: absolute;
}

@mixin fix-pos($top: auto, $bottom: auto) {
    top: $top;
    bottom: $bottom;
    left: 0;
    width: 100%;
    position: fixed;
}

//absolute center
@mixin abscenter($width, $height) {
    position: absolute;
    top: 50%;
    left: 50%;
    width: $width;
    height: $height;
    margin-left: -($width / 2);
    margin-top: -($height / 2);
}

// background cover
@mixin bg-cover {
    position: fixed;
    top: 0;
    right: 0;
    left: 0;
    bottom: 0;
    background:rgba(0,0,0,.6);
}